Electron emission coating mixtures



Patented Mar. 30, 1954 UNITED STATES ATENT OFFICE 2,673,387 ELECTRONEMISSION CGATING MIXTURES Gordon M. Forker, Lyndhurst, Ohio, assignor toGeneral Electric Company, a corporation of New York No Drawing.Application May 18, 1951, Serial No. 227,115

2 Claims. (01. 29-2514) 2 My invention relates to electric dischargedeadvantages of employing Cellosolve acetate as vices and more particulrly to electron emissive the solvent are found in the improvedcharacter, catho es therefor. More particularly my invenas well as theheavier Weight of the filling of tion relates to compos tions ofelectron emissive the electron emissive mixture in the cathode coil.coating mixtures useful for activating such In a given size coil, theweight of the emissive cathodes. material is increased from an averageof about My invention is particularly useful in connecmg. to about 5 mg.for Cellosolve acetate ticn with the application of electron emissivemixes as compared With amyl acetate mixes.

fl to "0116i Wire t o e p fii u fly However, even aside from theincreased Weight, colei-coil cathodes as employed in the conven- 1U isnoticeable that the Cellosolve acetate mix tional fluorescent lamps.Such cathodes are penetrates into, and more completely fills, the

composed of a refractory wire, such as tungsten, primary coil of thecathode. The material withwhich is helically wound into a primary coilin the primary coil fullv effective andis retained which is, in turn,helically wound. into a secondfor a long useful life, whereas anymaterial left ary 001 to constitute the coiled coil. It has been hangingon the outside of the coil becomes disthe DraCtiCe to st u 8 as y pplodged end. falls oil during operation of the lamp with an electronemission mixture comprising 2. containing the cathode. The improvedcharacsuspension of electron emissive material usually ter of th 1-111 rcoating i evidenced by the comprising alel'ne earth carbonates includingfact that the primary coil contains a higher probarium, calcium anistrontium carbonates which portion of solid slugs of the emissionmaterial may e u s y a double p e and a lower proportion of annularsegments. bonates and which are carried in suspension in Th e r ult maybe due, in part, t the f ct a cellulosic ester or ether binder such as asolu that since the Cellosolve acetate requires more ton ofnitro-cellulose in a solvent like amyl aceti t va or t it gives themixture time to tate- In subsequent m ufac u n steps, after sin: deeperinto the primary coil before it freezes the cathode has b n s in thelamp bulb 0 or sets. However, it is also fact that other solen e ope, ts a i activated y heating to vents, even some having slower evaporationrates break down the alkaline earth carbonates to the t c t t Such asdjacetone 1 corresponding oXides, the bi d being bu cohol and acetonylacetone, are not satisfactory.

out. I have obtained good results by employing In accordance with thepresent inventio I mixtures comprising a suspension of about havediscovered that materially improved results 13e 2 o grams of am i a thcarb nate in are obtaine When he ConventiOnal solvent of about 115 to145 ml. of a binder of nitrocellulose amyl ace-tote is replaced byCellosolve acet dissolved in Cellosolve acetate and having a (ethy Smonoethyl Ethel acetate)- viscosity of about 30-100 centipoises. Iprefer One O t a a a e of emp oy Ce to employ triple carbonates ofbarium, strontium solve acetate as the solvent in place of amy andcalcium. The composition of the triple acetate is that it makes a morestable mixture carbonate may be aried idely but good re because of itsslower evaporation rate (21 comit h b e obtained with proportions of pard t 6 on an ar itrary s ale where bu approximately 33.6 mole per centbarium, 31

acetate is s t t The amyl acetate mole per cent strontium and 30.4 moleper cent tures require frequent dilution as the solvent i i evaporates.The necessity of dilution is evi- A specific l by way of illu trati n, f

danced by a bridging of the emission mixture a mixture with which goodresults have been across the secondary coils of the coiled-coiledobtainedis t follgwjng:

cathodes. However, each dilution is likely to Th3 binder i prepared bymixing 2.1 kg. of go too with the result that the 0011 than isnitrocellulose with 147 kg. of Cellosolve ace- 9 filled with a 9 weightof w emission tate and rolling the mixture until the solution ismlxture- Another dlsadvamage of mlxtures complete. The solution is thenfiltered, checked ploying amyl acetate is that they tend to form for asolid content of 3.5-1.5 per cent and a viscrusts on the coatingequipment, such as that osity of 3e Seconds t 25 C in a #7 d p tdisclosed in Patent 2.54 t W- P- Za l cup, and adjusted if necessary. Amixture is which is as ned 13 e assignee Of the present then made of17.04 liters of the aforesaid binder invention. with 30 kg. of triplecarbonates of the alkaline Even more important, and wholly unexpected,5: earth metals. This mixture may be ball-milled for approximately 20hours. The mixture is then stored until ready for application tocathodes in any suitable manner such as that disclosed in the aforesaidPatent 2,545,909.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A coating composition for coiled-coil cathodes and consistingessentially of a suspension, in proportions corresponding to the statedamounts, of about 130 to 260 grams of finely divided alkaline earthcarbonates in about 115 to 145 ml. of a binder of nitrocellulosedissolved in ethylene glycol monoethyl ether acetate and having aviscosity in the range of about 30 to 100 centipoises.

2. The method of introducing activating alkaline earth materials oncathodes in electric discharge devices which comprises suspendingpowdered alkaline earth metal carbonate in a binder of nitrocellulosedissolved in ethylene glycol monoethyl ether acetate in proportionscorresponding to about 130-260 grams of carbonate in about 115-145 ml.of a binder of nitrocellulose dissolved in ethylene glycol monoethylether acetate and having a viscosity in the range of about 30-100centipoises, coating a coiledcoil cathode with said suspension, sealingthe cathode in said device, and activating the oathode by heating tobreak down the alkaline earth carbonate to the corresponding oxide andto burn out the binder.

GORDON M. FORKER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,791,301 Davidson Feb. 3, 1931 1,842,161 Fredenbaugh Jan. 19,1932 2,083,372 Guthmann June 8, 1937 2,223,977 Wamsley Dec. 3, 1940OTHER REFERENCES Handbook of Material Trade Names, Zimmerman and Lavine1946 pg. 95, Industrial Research Service, Dover, N. H.

1. A COATING COMPOSITION FOR COILED-COIL CATHODES AND CONSISTINGESSENTIALLY OF A SUSPENSION, IN PROPORTIONS CORRESPONDING OF ASUSPENSION, AMOUNTS, OF ABOUT 130 TO 260 GRAMS OF FINELY DIVIDEDALKALINE EARTH CARBONATES IN ABOUT 115 TO 145 ML. OF A BINDER OFNITROCELLULOSE DISSOLVED IN ETHYLENE GLYCOL MONOETHYL ETHER ACETATE ANDHAVING A VISOCITY IN THE RANGE OF ABOUT 30 TO 100 CENTIPOISES.